The present invention relates to a hydraulic cylinder for generating vibrations, and more particularly to a hydraulic cylinder for generating mechanical vibrations adapted for use in various mechanical workings performed through vibrations or adapted to be supplied to pile drivers, rock drills, and the like.
Generally known as the above-mentioned type of apparatus is an apparatus disclosed, for example, in Japanese Patent Provisional Publication No. 21580/72. This disclosed apparatus is arranged such that if the piston 101 of a hydraulically-actuated cylinder 100 has only one side thereof loaded with return force (e.g., by a spring 109) as shown in FIG. 1(a), a pipe 104 is connected to a hydraulic pressure chamber 102 on the other side not loaded with return force, through which pipe a hydraulic pressure fluid medium such as oil supplied from a reservoir 108 via a hydraulic pressure source 107 such as a pump P is supplied into and exhausted from the hydraulic pressure chamber 102 in an alternate fashion by means of control valve means 106, so that the pressure in the hydraulic pressure chamber 102 is alternately increased and decreased to cause reciprocating motion of the piston 101 in the axial directions thereof. While, if the piston has either side thereof adapted to be loaded with return force as in FIG. 1 (b), a hydraulic pressure medium is alternately charged into and discharged from the hydraulic pressure chambers 102 and 103 on both sides of the piston, by means of control valve means 106.
However, this conventional apparatus has the following defects: The cylinder 100 and the control valve means 106 are provided separately from each other and are connected with each other by means of pipes 104 and 105, with the result that when either of the hydraulic pressure chambers 102 and 103 of the cylinder 100, e.g., chamber 102 is being supplied with hydraulic pressure oil, the pressure in the chamber 102 is not elevated up to a sufficient level until the fluid of an amount corresponding to the inside volume of the pipe 104 becomes fully compressed, and on the other hand, when the hydraulic pressure chamber 102 is connected with the exhaust line, there occurs a time lag in the decrease of pressure in the chamber by an amount corresponding to the time required for the expansion of said fluid. That is, such conventional vibrating cylinder has its operating motion delayed in proportion to the volume of the fluid present in the connection pipe(s), and consequently when the cylinder is operated at a high vibration frequency, it can difficultly have a required amplitude of vibration. Further, if a high-output vibrating cylinder is used, a considerably large amount of hydraulic energy is consumed for compressing the fluid in the pipe(s) to supply hydraulic pressure to the cylinder.